\[LeftBracketingBar](((δ^2)ψ)/(δ (z^2)))\[RightBracketingBar]<<\[LeftBracketingBar](((δ^2)ψ)/(δ (x^2)))\[RightBracketingBar],\[LeftBracketingBar](((δ^2)ψ)/(δ (y^2)))\[RightBracketingBar],2k\[LeftBracketingBar]((δψ)/(δ z))\[RightBracketingBar](Subscript[∇, t]^2)ψ+j 2k((δψ)/(δ z))=0